JP2815091B2 - Manufacturing method of slender superconductor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a method for producing a coated superconducting wire and ribbon.

Description of the Prior Art Since the invention of superconductivity in 1911, well-known superconductor materials are essentially metallic elements (eg, Hg, the first known superconductor) or metal alloys (eg, Hg). Nb ₃ G
e, probably the substance with the highest transition temperature _Tc known before 1986).

Recently, superconductivity has been discovered in new materials. For example 19
See Physica, Vol. 126, p. 275, B. Batlogg, 1984. This is examining the superconductivity of barium lead bismuth oxide. Or the 1986 Zeitschrift Füzibj-Condensed Matter (Zeitschr. F. Physi
See kB-Condensed Matter, Vol. 64, p. 189, JGBednorz and KAMuller. This reports the superconductivity of lanthanum barium copper oxide.

In particular, the latter report has fueled worldwide research activity and has rapidly made significant progress. Above all, this progress is Y-Ba
-Cu-O-based composition has led to the discovery that can have superconductive transition temperatures T _c above 77K, the boiling point of liquid nitrogen (19
March 2, 1987 Physical Review Letters (Phy
Letters), Vol. 58, p. 908, MKWu et al. and p. 911, PHHor. In addition, this progress has led to the identification of material phases for the observed high-temperature superconductivity and the discovery of techniques and compositions for forming bulk samples of materials that can be substantially single-phase materials and have a _Tc of greater than 90 K (US Patent Application No. 024,046, Mar. 10, 1987 Patent application "Devices and systems based on new superconducting materials" filed by BJ Batlog, RJ Cava and RBvan Dover The excitement of the scientific and technological world, caused by recent advances in superconductivity, is due, in part, to the potentially enormous technical impact of superconducting materials at temperatures that do not require the cooling of expensive liquid helium. Things. Liquid nitrogen is generally considered to be a very convenient cryogen. Therefore, achieving superconductivity at liquid nitrogen temperature has long been
It was a goal I had explored for many years that I could hardly reach.

Although this goal has now been reached, there are at least one obstacle that must be overcome before new oxide high _Tc superconductors can be used in many technological applications. Especially,
Techniques must be developed to form superconductors having technically usable shapes.

Oxide superconductors are easily manufactured in powder and are processed in various forms such as globules, disks and rings by ceramic technology. U.S. Patent Application No. 025,913, filed March 16, 1987, by EMG Gyorgy and DW Johnson Jr., entitled "Apparatus Constituting Ceramic Superconductor and Its The "Method of Manufacturing" discloses a technique for making a ceramic superconductor having one relatively small dimension (5 .mu.m-1 mm). Such fibrous and sheet superconductors include fine rods, filaments, tapes and sheets, which include bitter magnets, transmission lines,
Applicable to various devices such as rotating machines, maglev trains and fusion devices.

Possibly, metal superconductors such as Nb ₃ S
The most economically important application of n) is in the form of superconducting magnet wires. Magnets incorporating such wires have been applied in many scientific laboratories, and among them, the proposed large particle accelerator, the so-called “superconducting collision accelerator” (Superc
on superconducting wire. Conventional superconducting wires generally have a mixed structure with superconducting filaments embedded in a normal (ie, non-superconducting) metal, typically copper. It performs several important functions in such a wire: providing a bypass for electrical conduction paths, providing a means of conducting heat in local magnetic flux movements, and increasing the mechanical strength of the wire.

For an overview of the potential applications of superconductors, see eg
Bee, published by Plenum Press in 1977
"Application of Superconductivity: SQUIDs and Machines" edited by BB Schwartz and S. Fonter and "Superconducting Materials Science" edited by S. Fonell and BB Schwartz published by Plenum Press, 1981 , Metallurgy, manufacturing and applications. " Their applications are power transmission lines, rotating machinery and fusion power generation, MHD power generation, particle accelerators, maglev trains, superconducting magnets for magnetic separation and energy storage, etc. Heretofore, practical and possible applications have been considered for conventional (non-oxide) superconductors. If If utilized instead wires of high T _c relatively low T _c superconductive wire ever, the application of superconducting described above are expected to be highly advantageous. Accordingly, an object of the present invention is to provide a method of producing an elongate superconductor such as superconducting tape or wire of a high T _c.

SUMMARY OF THE INVENTION The present invention is a method of making an elongated superconductor in which the superconducting material is a sintered oxide (typically a cuprate), usually surrounded by metal (clad). The cupric hydrochloric acid of interest here is typically of nominal composition, M _3-m M ' _m Cu ₃ O _9-δ
Where M is mainly Ba (all or part of Ba may be replaced by elements such as Ca and Sr), and M ′ is Y, L
a, Eu, Lu and Sc are one or several types. m is about 1
Where δ is typically in the range of 1.5 to 2.5, with a maximum difference of about 10% between M and M 'from the nominal stoichiometric composition.
Currently preferred cuprates have a nominal composition Ba ₂ YCu ₃ O _9-δ ,
Here, δ is about 2.1. This material is also called (Ba, Y) cuprate.

Such strips are often referred to herein as "wires" or "tapes." The term is not limited, for example, with respect to the cross-section of a wire-like object (eg, such an object conveniently has a non-circular cross-section and may be a number of coaxial superconductors).

The method of the present invention comprises the steps of forming an intermediate consisting of a cladding material surrounding some of the oxide powder, forming an elongated body by means of cross-sectional reduction from the intermediate (eg, through a wire drawing die or a rotating device), And a heat treatment step of the elongated body.

The strip is often processed in a molding process prior to heat treatment, whereby the strip is substantially brought into the shape used. For example, the elongated body is spirally wound on a mandrel in the form of a magnetic coil.

The intermediate consists of an oxide powder surrounded by a diffusion barrier, which is usually surrounded by a metal jacket. Usually the metal jacket is a copper tube, the diffusion barrier consists of a thin-walled silver tube in a thin-walled Ni tube, and the oxide powder is contained in this thin-walled silver tube. If the metal jacket material is usually inert with respect to the oxide, no diffusion barrier is needed. Ag is an inert metal, at least for (Ba, Y) cuprates.

The heat treatment of the elongated body results in sufficient sintering of the oxide powder, and after completion of the heat treatment, the chemical composition of the sintered oxide is reduced to the sintered oxide powder or clad made from this powder. This is done so that the superconductivity of the unsintered oxide is within certain limits.

The oxides are relatively unstable with respect to their oxygen content (for example, they easily lose oxygen when heated to relatively high temperatures) and are superconductive only within a relatively narrow range of oxygen content. Has the property. Thus, the present invention treats, after completion of the heat treatment, the oxygen content of the sintered material such that the material is at a temperature of technical significance, typically above 77K, and within a range such that it becomes a current carrying conductor. There is a need. These treatments include oxygen donor material (eg,
With the arrangement of BaO ₂ or AgO), the hermetic sealing of the intermediate in air or at a higher oxygen partial pressure, or a hole in a tube or perforated tube, usually metal cladding, placed in a powdered substance or barrier Is the direct insertion of oxygen through the diffusion barrier into the space.

In particular, the method of the present invention can be used to produce single fiber superconducting wires, multi-fiber superconducting wires of various cross-sectional shapes, or tapes and ribbons containing superconducting elements. Many systems and devices conveniently comprise the wires or tapes of the present invention. These superconductors typically allow operation at temperatures higher than the operable temperature of conventional superconducting wires. Typical examples of wire or tape devices of the present invention are superconducting solenoids, and typical examples of such systems are particle accelerators, maglev transport systems, fusion reactors including magnetic confinement, and transmission lines. The superconductor of the present invention can also be used as a signal transmission line in an electronic device.

The preferred embodiment becomes superconductive at temperatures of T _c > 77K. T
An example of a _c> 77K substances are Ba ₂ YCu ₃ O _6.9. It has recently been reported that some oxides (cuprates) of the type described here have exhibited signs of superconductivity at temperatures above 200 K, which can be as high as 240 K or more. See, for example, page 6 of the New York Times on Saturday, March 28, 1987. This reports observations made at Wayne State University. See also the paper entitled "Observation of the Inverse AC Jusefson Effect at 240K" by JTChen et al. Similar claims have been made by researchers at Berkeley University. The method of the present invention for making elongated oxide superconductors, usually consisting of metal cladding, is widely applicable to forming such superconductors from oxide powders and has been used particularly in experiments at Wayne State University and Berkeley University. It can be applied to form such a superconductor from a cuprate powder such as (La, Y) cuprate.

Description of the Examples For the same reasons as conventional superconducting wires, wires and tapes based on oxide superconductors are also advantageously composites, usually consisting of metal cladding, surrounding the oxide superconductor. The reason why the oxide superconductor is buried in a normal metal which is not employed in the conventional wire is that it is necessary to sufficiently eliminate the interaction between the superconducting material and the surroundings.

For example, it has been found that the oxygen content of some copper oxide powders in air decreases with time, even at room temperature. Such a decrease in oxygen content impairs the superconducting properties of the material. In addition, there is the potential for adverse reactions with water vapor, CO ₂ and other environmental gases. Another reason is that there is generally a need for mechanical support of a relatively brittle sintered oxide superconductor to withstand the Lorentz force due to the interaction of the current flowing through the superconductor and the magnetic field created by this current. .

FIG. 1 shows a cross-sectional view of a typical wire 10 of the present invention.
Here, 11 is a sintered oxide superconducting filament, 12 is a normal metal (eg, Cu) jacket, and 13 and 14 are two diffusion barrier layers. The diffusion barrier layer 13 is relatively inert with respect to oxygen and other oxide components (eg, Ag, Au, P
d), and the diffusion barrier layer 14 is basically a metal jacket 1
2 and a material that does not form an alloy with the material of the diffusion barrier layer 13. If the metal jacket 12 is Cu and the diffusion barrier layer
If 13 is Ag, the diffusion barrier layer 14 is preferably Ni.

FIG. 2 also shows a cross section of a typical multifilament wire 20. Here, each of the three sintered oxide filaments 21 is surrounded by an expanded barrier layer 23 and is usually embedded in a metal jacket 22. Another embodiment (not shown) consists of an oxide superconducting filament surrounded by a dielectric layer, which is also surrounded by a tubular oxide superconductor and (if necessary, a diffusion barrier). Coaxial assemblies are usually surrounded by metal cladding.

FIG. 3 shows a tape 30 of the present invention. 31 is a sintered oxide superconductor, 33 is a diffusion barrier layer, and 32 is usually a metal jacket. Other exemplary tapes of the invention (not shown)
Includes a number of ribbon-shaped superconductors, usually embedded in a metal cladding.

An important aspect of the present invention is the processing of superconductors (filaments, ribbons) having superconducting properties, usually in a metal cladding. The most important of these properties are
The transition temperature T _c (here considered the highest temperature at which the DC resistance is zero). Desirable is T _c > 77K. Further, it is desirable that the transition temperature of the synthetic clad body is basically close to that of a bulk ceramic body having the same composition (90% or more thereof).

This processing step is typically a multi-step procedure comprising some or all of the following steps. The oxide starting material can be manufactured by a known process. This treatment typically involves the addition of a metal oxide, hydroxide, carbonate, hydrate, oxalate or other reactive precursor in an appropriate ratio to obtain a predetermined final mixture. the step of mixing, the slurry filtered showing steps, steps to scrap dried cake, and sintering the debris in an atmosphere containing O ₂ and (typically 900
C. and held at this temperature for 2 hours, cooling the furnace). The burned debris is reground, re-crushed and sintered as necessary to achieve homogeneity. The homogeneous material is then crushed to produce a powder of a predetermined mesh size.

The powder so made is optionally heat treated (typically 300-700 ° C., 10 minutes to 2 hours, O ₂ partial pressure 0.1-10 at.
m), and / or optionally mixed with an oxygen donor powder (eg, a silver oxide such as well separated AgO) or a small amount of a growth inhibitor (Ag powder). The powder is then usually packaged in a metal (eg, Cu, Ag, high strength heat treated steel) outer jacket, and optionally a container consisting of a diffusion barrier (eg, Ni and Ag). The surface of the outer jacket is protected from oxidation by a suitable material (eg Ag) layer. The container is then closed (e.g., fastened or welded) or by any other suitable means to prevent the oxide powder from deteriorating, and at room temperature or other (typically high) temperatures, Perform some suitable section reduction steps, such as a continuous drawing step, or a rotating step, a swaging step, or an extrusion step. The elongated mixture thus made is then optionally shaped (eg, coiled onto a mandrel).

Next, the elongated body (after or before shaping) is heat-treated to allow sufficient sintering of the oxide powder. The heat treatment desired here is typically to heat the elongated body to a temperature in the range of 700-950 ° C. and hold at this temperature until sufficient sintering takes place (typically 0.1-100 hours); Slowly 300
Cooling to within a temperature range of 700700 ° C. and holding at this temperature until a predetermined oxygen content is established in the sintered material (typically 1 to 24 hours).

If the mixture contains a normal metal that is precipitation hardenable (eg, high strength heat treated steel), a known precipitation hardening treatment may be performed after the above heat treatment.

The need to bury oxide superconductors in metals usually and the tendency of the related oxides to lose oxygen at relatively high temperatures (and absorb oxygen at lower temperatures) requires new processing. Among these processing features is the need to prevent contact between the powder and substances that oxidize at the temperature during processing. Currently a desirable technique to prevent such contact is to surround the oxide with a thin layer of a suitable non-reactive material, for example Ag or Au. Various materials such as Pd, Ru, Rh, Ir, Os, Pt, Ni and stainless steel are available depending on the situation. This layer is called a diffusion barrier.

In some cases, the wire (or tape) of the present invention
Need not include a diffusion barrier. For example, if the metal jacket is usually made of a metal that is substantially inert with respect to oxygen and does not harm oxides, a diffusion barrier is not required. Ag is such a non-harmful normal metal, at least for the (Ba, Y) cuprate.

The new process comes from the need to keep the oxygen content of the sintered powder within a relatively narrow range. Sintering of the oxide particles is often performed at temperatures above 700 ° C. It has been found that oxides often lose oxygen at such temperatures at normal pressure. Accordingly, the method of the present invention typically has features configured to prevent loss of oxygen from the space containing the powder. This is typically the highest possible O ₂ before heat treatment.
Hermetically sealed elongated body with pressure, or during the heat treatment, it is completed by performing it connects the high pressure O ₂ gas reservoir at the end of the elongate body, or a relatively high pressure (e.g. 2～20Atm) heat treatment in the oxygen You. In the latter case, it is usually necessary to prevent oxidation of the metal surface. Thus, usually the metal jacket is made of a relatively inactive material (eg Ag),
Or the jacket surface is relatively inert (eg, A
g, Au or Pd).

Instead of the treatment to prevent the loss of O ₂ from the space occupied by the oxide powder, or in addition to the treatment method of the present invention consists of the treatment of introducing O ₂ into the space. Typically these treatments are forced flow of O ₂ into the space,
Alternatively, it is performed by introducing an oxygen donor substance (for example, BaO ₂ or AgO powder) into the space. Such donor material releases oxygen during the heat treatment, and the released oxygen is available for incorporation into the superconducting oxide.
Materials that can be used as oxygen donors must not be harmful to oxide superconductors. That is, it is apparent to those skilled in the art that the reaction must not basically react with oxygen so as to impair the superconducting characteristics.

In some cases, after performing a size reduction operation, it is possible to place a perforated tube in the powder space of the intermediate due to the presence of perforated channels in the powder. O ₂ can be easily supplied through this channel. Also, in some cases, it is advantageous to drill holes at appropriate intervals in the usual metal surrounding the oxide powder and to contact the perforated strip with oxygen during heat treatment.

As mentioned above, superconducting oxides can be used in the atmosphere or at moderate (eg, 1 atm) O ₂ pressure and at relatively high temperatures (eg, about 900
° C) often releases oxygen when heated. On the other hand, these oxides often absorb oxygen when cooled to intermediate temperatures. This thermodynamic property of oxides can form the basis of a new heat treatment. There, the partial pressure of oxygen in the oxide powder is adjusted during the heat treatment to maintain an optimum oxygen stoichiometry. Processing details often depend on powder composition as well as temperature, but with the new variable O ₂ pressure heat treatment the (relatively hot) sintering step is typically relatively high (eg, 1.5
20 atm) was carried out in O ₂ partial pressure and subsequent (relatively low temperature)
Step is carried out at relatively low (e.g., 1-5 atm) O ₂ partial pressure, typically slow cooling from a high temperature to low temperature is desired.

As will be appreciated by those skilled in the art, the temperature at which a particular heat treatment step is performed will depend on the length of the processing step. Thus, if the sintering time is relatively long (eg, 24 hours or more), the sintering step may be performed at a relatively low temperature (eg, 70
0 ° C). Typically the sintering temperature is 600 ~ 1100 ℃
The time is between 0.1 and 1000 hours. The time and temperature of the sintering step also depend on the size of the oxide particles. By increasing the thermodynamic driving force to the sintering process, small particles allow for reduced time and / or reduced temperature. Thus, generally, in the practice of the present invention, relatively small particle size powders (eg, having an average diameter of
2 μm or less is desirable, and 0.5 μm or less is more desirable).

Conveniently the oxide powder used in the practice of the present invention has a stoichiometric composition. This means that bulk ceramic superconductors made from such powders have compositions related to high temperature superconductivity. We have found that, at least in some places, the milling (eg, ball milling) process used to create particles of a given mesh size, in addition to deforming the material, can also cause a change in composition. For this reason, in some cases,
Prior to making the powder an intermediate, a suitably sized powder is subjected to a relatively low temperature (eg, 300-700 ° C.) oxygen anneal (typically
Exposure to oxygen (0.1-10 atm) for about 10 minutes to 2 hours is desirable.

As mentioned above, in many cases, it is desirable to shape the elongated clad body made from the intermediate body by a suitable known cross-sectional reduction process before heat treating the elongated body.
Heat treatment typically results in sintering of the oxide powder, thus reducing the ease of forming superconducting elements. Heat treatment, on the other hand, often results in softening of the usually metallic parts of the elongated body. Prior to sintering, it is desirable to use a precipitation hardenable conventional metal as the cladding material in order to make the superconductor of the present invention easy to form and have good mechanical strength. As is known, such alloys (eg, high strength heat treatment (maragi
ng) steel or Cu-Ni-Sn spinodal
Alloy) can be hardened by a relatively low-temperature treatment after the wire drawing and shaping steps. Such treatments typically do not affect the superconducting properties of the elements of the sintered oxide. If such treatment is applied to a suitably shaped superconducting wire or tape (eg, a helical coil), an element or device is created that simplifies handling and subsequent processing.

Example 1 Powder of nominal composition Ba ₂ YCu ₃ O _6.9 (average particle size is about 2.5
μm) is made by known processes and
It is exposed to annealing at 600 ° C. for 15 minutes. The bulk superconductor made from the powder prepared in this way has a T of about 93K.
_c (R = 0). Silver tube (0.250 inch outer diameter (= 6.35
mm), the wall thickness of 0.030 inch (= 0.762 mm)) is filled with this powder and both ends of the tube are sealed. The preform made in this way has a diameter of 0.060 inch (= 1.524) at room temperature.
mm) with 15 passes. The wire is coiled on a 1.5 inch (38.1 mm) diameter mandrel. At this stage, the coil does not exhibit superconductivity. The coil is then heat treated as follows: hold at 900 ° C. for 8 hours, cool in furnace to 600 ° C., hold at 600 ° C. for 4 hours, cool in furnace to about 350 ° C. These processes are carried out in a fluidized O ₂ all about 1 atmosphere. The coil is then removed from the furnace and a portion is tested by a standard DC resistance measurement. The result of this measurement is shown in FIG. As can be seen, this wire has full superconductivity at 91K. The sintered oxide is removed from a portion of the coil, powdered, and analyzed by standard powder X-ray techniques. The spectrum of this material is essentially the same as that of the sintered bulk sample of the mixture Ba ₂ YCu ₃ O _6.9 .

[Example II] A coil is basically prepared in the same manner as in Example I. However, outer diameter 3/16 inch (= 4.76mm), inner diameter 1/8 inch (= 3.1
8mm) copper tubing is used. Diffusion barrier is thick first
It is formed by wrapping a 0.002 inch (= 0.0508 mm) Ni foil in a copper tube and then wrapping a 0.002 inch (= 0.0508 mm) thick Au foil. The thus formed normal metal jacket is then filled with powder. A portion of this wire is measured. The superconducting properties are essentially the same as for the wire of Example I.

Example III A coil is basically made as described in Example I. However, instead of a silver tube, the outer diameter is 3/16 inch (= 4.76m
m), a copper tube with an inner diameter of 1/8 inch (= 3.18 mm) is used. No superconductivity was observed in the coil above 77K.

[Example IV] The coil is basically prepared as described in Example I. After bending the coil, but before heat treating the coil, the Ag cladding is drilled at approximately 1 inch (= 25.4 mm) intervals. The heat-treated coil is superconducting, about 91
K has a T _c (R = 0).

[Example V] The coil is basically prepared as described in Example II. However, a Pt foil of 0.002 (= 0.0508 mm) inch is used instead of the Au foil. A portion of this wire has been measured and shows a broad transition to a low resistance state, ending at about 30K.

Example VI A tape is prepared basically as described in Example I. However, the sealed, powder-filled Ag tube is lengthened by rolling to 0.010 inch (= 0.254 mm) thickness on a conventional rolling mill.

[Example VII] The coil is basically prepared as described in Example I. However, AgO powder (average particle size 1.3 μm) is mixed with cuprate powder (AgO 20% by weight). This coil basically had a superconducting transition as shown in FIG.

[Brief description of the drawings]

1 and 2 are cross-sectional views of a typical monofilament and multifilament wire of the invention, respectively; FIG. 3 is a diagram showing the tape of the invention; FIG. 4 is a spiral coil according to the invention. FIG. 5 shows a superconducting magnet; FIG. 6 shows resistivity as a function of temperature for a clad oxide superconductor of the present invention. 10 Wires 11 Oxide superconducting filaments 12, 22, 32 Metal jackets 13, 14, 23, 33 Diffusion barrier layer 20 Multifilament wires 21 Oxide filaments 30 Tape 31 ... oxide superconductor 50 ... superconducting magnet 51 ... mandrel 52 ... superconducting magnet wire

──────────────────────────────────────────────────続 き Continued on the front page (72) Richard Carly Sherwood, Inventor United States, 07974 New Jersey, New Providence, Vista Lane 8 (72) Inventor Robert Bruce Van Dover United States, 07922 New Jersey, Berkeley Heights, Emerson Lane 300 (56) References JP-A-63-225409 (JP, A) JP-A-63-232210 (JP, A) JP-A-1-100003 (JP, A) (58) Fields investigated (Int. . ^6, DB name) H01B 12/00 - 12 / 16,13 / 00 561, 563,565 C04B 35/00 - 35/22 5G321,4G030

Claims (8)

(57) [Claims] 1. A method comprising: (a) providing an oxide powder; (b) forming an intermediate having a metal cladding surrounding the oxide powder; and (c) means for reducing a cross-section. Forming a slender body from the intermediate; and (d) heat-treating the slender body. (E) The oxide powder has a _Tc (R = 0) of 77K. (F) a portion where the metal clad comes into contact with the oxide powder is silver; and (g) in the heat treatment step (d), the oxide powder is The elongated body is sintered in contact with an oxygen-containing atmosphere, and the obtained sintered oxide has the same powder X-ray analysis spectrum as that of the copper-containing superconducting compound, and T _c (R = 0) is 77K or more A method for manufacturing an elongated superconductor. 2. The method according to claim 1, wherein said oxygen-containing atmosphere is an oxygen atmosphere. 3. The method according to claim 2, wherein the pressure of oxygen is 1 atm or more. 4. The chemical composition of the copper-containing superconducting compound having T _c (R = 0) of 77 K or more is YBa ₂ Cu ₃ O _x (x is substantially equal to 7). Method 1. 5. The heat treatment of the elongated body is performed by holding the elongated body at a temperature of 700 to 900 ° C. for 0.1 to 1000 hours until the elongated body is sufficiently sintered. To 3
The elongated body is cooled to a temperature in the range of 00 to 700 ° C. and the elongated body is kept in a temperature range of 300 to 700 ° C. until an oxygen concentration in which the T _c (R = 0) is 77 K or more is achieved in the sintered oxide. 5. The method of claim 4, wherein the method is performed by maintaining. 6. The method according to claim 1, wherein the metal clad is a silver clad. 7. The method according to claim 1, further comprising the step of shaping the elongated body before the heat treatment step (d) is completed. 8. The method of claim 7, wherein the step of shaping the elongated body is a step of shaping the elongated body into a helical coil.